The IMOD software package provides tools for generating, viewing, and analyzing 3-dimensional (3-D) image data, with a focus on tools for electron tomography, which involves the reconstruction of the interior of a specimen from a series of tilted views obtained with an electron microscope. The use of tomography has been growing rapidly in cell and structural biology research, and there is potential for even wider use in diverse areas of biomedical research. The long-term goals of this project are 1) to continue the development of the IMOD software so that it will continue to offer a powerful and attractive package for tomographic reconstruction, even as methods and equipment evolve, and 2) to provide a resource that can be both used and built upon by others in the biological microscopy community. One aim is to work towards complete automation of the process of tomographic reconstruction, which includes automating the alignment of images and reducing user effort in other steps of the process. A second aim is to add new features in response to users' needs. This work includes providing access to new features in the user interface for tomographic reconstruction and other data processing, and enhancing the graphical modeling program in IMOD for better analysis and visualization of 3-D data. User interfaces and documentation will also be upgraded to make the software easier to use. A third aim is to improve and modernize some aspects of the underlying source code and to maintain the availability of the software on multiple platforms (Linux, Microsoft Windows, and Macintosh OS X). This work will enable the software to use the power of modern computers more efficiently and make it function better with the large data sets that are becoming increasingly common.